JP2015504955A - Heat treatment of water-absorbing polymer particles in a fluidized bed at a fast rate of temperature rise - Google Patents

Abstract

The present invention relates to a method for heat-treating water-absorbing polymer particles at a temperature rise rate of 150 ° C. or higher in a fluidized bed dryer at a high temperature rising rate, and a fluidized-bed dryer for heat treating water-absorbing polymer particles in a continuous or batch mode. And heat treated polymer particles obtained by the process of the present invention. [Selection figure] None

Description

  The present invention relates to a method for heat-treating water-absorbing polymer particles at a temperature rising rate of 150 ° C. or higher in a fluidized bed dryer, and a fluidized-bed dryer for heat treating water-absorbing polymer particles in a continuous or batch mode. And heat treated polymer particles obtained by the process of the invention.

  Water-absorbing polymers, i.e. polymers that absorb aqueous liquids, e.g. water, blood or urine, are important in modern disposable hygiene articles such as disposable diapers, adult incontinence products, sanitary products or first aids Is an element. Particularly useful are so-called superabsorbent polymers that can absorb at least 50 times their own weight of water and aqueous solutions (based on deionized and distilled water) by hydrogen bonding with water molecules ( superabsorbent polymers (SAP), that is, a normal water-absorbing polymer for forming a hydrogel. Many SAPs can absorb more than 100 times their weight and retain a significant amount of absorbed water even under pressure.

  Such a water-absorbing polymer is usually a small amount of at least one cross-linking agent, i.e., two such as N, N'-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol di (methacrylate) or triallylamine. In the presence of functional or polyfunctional monomers, usually ethylenically unsaturated monomers such as, for example, α, β-unsaturated carboxylic acids such as, for example, acrylic acid, their sodium, potassium, ammonium salts or mixtures thereof Is prepared by polymerizing. These difunctional or polyfunctional monomers introduce light crosslinks in the polymer chain, making the water-absorbing polymer water-insoluble but water-absorbing.

  Powdered and fine superabsorbers are produced by two main methods. According to the first method, radical polymerization is carried out in an aqueous monomer solution (so-called solution polymerization), pulverized, dried, powdered and sieved to produce a gel with the desired particle size. According to the second method, the monomer (or its aqueous solution) is dispersed in a hydrophobic organic solvent by means of emulsifiers (referred to as suspension polymerization) or colloidal polymerization and radical polymerization. After azeotropic dehydration of residual water from the reaction mixture, the polymer product is filtered and dried.

  For example, to improve and / or fine tune further properties of the water-absorbing polymer such as retention capacity, gel strength, absorption rate, absorbency under load, etc. The dried and dried polymer particles are optionally further heat treated in the presence of a surface modifier. Such heat treatment processes are described in, for example, Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5.

  Several devices and methods are described in these applications and patents for heating polymer particles, such as, for example, hot air dryers, heated screw devices, plate dryers, fluidized bed heater / dryers and contact dryers. Preferably, a contact dryer is used for the surface SAP particles. In a contact dryer, undesired wear and product degradation may occur due to agitation and shear.

  On the other hand, in known fluidized bed dryers for the purpose of heat treating excellent absorbent polymer particles, heat treatment is very important in various aspects.

German patent invention No. 4020780 European Patent No. 0979250 International Publication No. 94/20547 International Publication No. 2006/082421 International Publication No. 2007/074108

  First, in order to be accompanied by a suitable heat treatment, a temperature range that is very close to the temperature range (exceeding about 200 ° C.) at which exothermic self-decomposition of SAP frequently occurs and needs to overlap the temperature range is necessary. Depending on the conditions of heat exchange in the fluidized bed, this may lead to an uncontrollable exothermic reaction, especially if the particles are not fluidized properly or larger particles (eg agglomerated) are fluidized bed dried. If it enters the machine or is formed in a fluidized bed dryer, it can lead to ignition. In either case, the raw material for the water-absorbing polymer particles remains on the hot bottom plate of the fluidized bed dryer and is heated there, thus starting an exothermic reaction.

  Second, the majority of SAPs having a particle size of less than 250 μm are washed from the fluid bed dryer before being properly heat treated. Therefore, this washed fraction cannot be simply mixed with the processed raw material. Rather, it must be mixed in a further process before being mixed with the heat treated product, or alternatively it may be reused as microparticles for the polymerization process. In any case, it is not desirable for the raw material to be washed to have a high fraction because further processing is required, reducing the overall yield and quality of the product and the throughput of the product.

  Third, usually during the heat treatment, the liquid retention capacity in saline measured by centrifuge retention capacity (CRC) after centrifugation is significantly reduced, and the adsorption against pressure; AAP) does not reach the desired level. Thus, it is generally difficult to obtain a product with both high CRC and high AAP. Furthermore, the water permeability of heat-treated products, as indicated by permeability under load (PUL) and saline flow conductivity (SFC), is usually poor.

  Accordingly, it is an object of the present invention to provide a method for heat treatment so that polymer particles have both good quality water absorption characteristics and water immersion characteristics. This method further preferably allows the polymer particles to be heat treated substantially uniformly at high temperatures without risking exothermic decomposition of the polymer. Preferably, the method allows heat treatment of the superabsorbent polymer particles with a short residence time even in continuous mode.

  Surprisingly, when the polymer particles in the fluidization chamber of a fluidized bed dryer are heated at a fast rate of temperature, that is, at a rate of at least 10 degrees per minute, the product performance of the heat treated product and the operation of the heat treatment It was found that both efficiency improved significantly.

  The present invention thus provides a method for heat-treating water-absorbing polymer particles at a temperature Tp1 of 150 ° C. or more, wherein the polymer particles are used in the fluidization chamber of a fluidized bed dryer from the initial particle temperature T0 of 50 ° C. or less. It is heated to a temperature Tp1 at a heating rate of at least 10 ° C. per minute. The rate of temperature increase is at least 11 ° C., 12 ° C., 13 ° C., 14 ° C., 15 ° C., 16 ° C., 17 ° C., 18 ° C., 19 ° C., 20 ° C., 21 ° C., 22 ° C., 23 ° C., 24 ° C. It is preferable that it is 25 degreeC. The particle temperature Tp1 is preferably in the range of 170 ° C. to 245 ° C., more preferably in the range of 190 ° C. to 235 ° C., which includes 195 ° C., 200 ° C., 205 ° C., 210 ° C., 215 ° C., 220 or 225 ° C. to 230 ° C. and 195 ° C. to 200 ° C., 205 ° C., 210 ° C., 215 ° C., 220 ° C., 225 ° C. or 230 ° C. are included. Preferably, the polymer particles have an initial particle temperature T0 to a temperature Tp1 of less than 20 minutes, more preferably less than 10 minutes, even more preferably less than 7.5 minutes, even more preferably less than 5 minutes. It is heated inside. The particle temperature is measured vertically by at least one PTF thermocouple in the center of the fluidized product. Suitable thermocouples are commercially available, for example, from ABB Automation Products GmbH (Alzenau, Germany) under the trade name SENSYCON. Suitable thermocouples are commercially available, for example, from ABB Automation Products GmbH (Alzenau, Germany) under the trade name SENSYCON.

Heat treatment of the polymer particles is accomplished by contacting the polymer particles with at least one gas stream having a temperature Tg greater than 150 ° C. Preferably, the polymer particles are in contact with at least one gas stream having a temperature Tg above 150 ° C. and up to 320 ° C. within the fluidization chamber of the drying chamber, said drying chamber comprising at least one fluidization chamber. The fluidization chamber opens downwardly into the at least one lower plenum chamber through the at least one gas distribution bottom plate, the gas distribution bottom plate flowing upward gas flow from the lower plenum chamber to the fluidization chamber. Having an opening formed for the purpose. The temperature T _g of the at least one gas stream is preferably in the range from 150 ° C. to 300 ° C., more preferably in the range from 180 ° C. to 295 ° C., most preferably in the range from 210 ° C. to 290 ° C., said temperature Is measured by at least one PTF thermocouple located 40 cm below the bottom plate, and in a continuously operating fluidized bed dryer, the thermocouple is located in the lower plenum chamber of the fluidization chamber, while the batch operated flow In a layer dryer, not only is the thermocouple normally located in the plenum below the bottom plate, it may be located in a conduit that delivers hot gas to the plenum. The surface gas velocity of the hot gas stream in the fluidized bed is preferably in the range of about 0.1 to about 0.57 m / s. More preferably, the surface gas velocity is in the range of about 0.15 to about 0.55 m / s, more preferably in the range of about 0.2 to about 0.5 m / s, most preferably about It is in the range from 0.3 to about 0.4 m / s. Superficial gas velocity v _s is based on the type of micropore plate for inlet gas velocity v _a and a predetermined pressure drop in the lower base plate, is calculated by the following equation 1.

Here, v _cor is a correction factor for a certain predetermined bottom plate and a certain predetermined pressure drop. The correction factor is obtained from a specific pressure drop curve for the appropriate type of bottom sheet provided by the bottom plate manufacturer.

Meters inflow velocity v _a of the per second is given according to the following equation.

  Where V is the gas volumetric flow rate in cubic meters per hour at the operating temperature and A is the square meter area of the bottom plate.

By employing a surface gas velocity within the range, it is possible to treat the polymer particles with a hot gas stream having a temperature near, or close to, or above the decomposition temperature of the polymer, Thus, particle temperatures in excess of 200 ° C. and / or very fast heating of polymer particles, for example, rates of 15 ° C. or more per minute, are possible, but even with continuous processing operating over several months, Do not face the problem of disassembly.
Also, by changing the surface gas velocity in the above range according to the specifications of the desired product, it is possible to adjust the size and amount of fine particles cleaned during the heat treatment, so that the overall product yield It is possible to save the trouble of subsequent size adjustment without lowering the size more than necessary.

  In the present invention, the term “heat treatment” includes heat treatment of water-absorbing polymer particles with or without a crosslinking agent for surface crosslinking (also called post-crosslinking).

  Surprisingly, it has been found that if the method of the present invention is employed, the product performance of the water-absorbing polymer particles can be significantly improved without the use of a surface modifier such as a surface cross-linking agent.

  In the present invention, the polymer particles in the fluidized bed preferably move along the substantially horizontal longitudinal axis of the fluidizing chamber during the heat treatment, and are conveyed from the product introduction port to the product discharge port. go. In fluidized bed dryers for heat treated water-absorbing polymer particles found in state-of-the-art technologies, such as Wurster and Glatt-Zeller dryers, the hot gas flow and polymer particle flow flow in substantially parallel. However, in the present invention it is preferred that the polymer particle stream and the at least one hot gas stream substantially intersect each other. The crossing angle between the direction of the polymer particle product stream inside the fluidization chamber and the direction of at least one hot gas stream entering the fluidization chamber through an opening from the lower plenum chamber in the at least one gas distribution bottom plate is 15 The range from ° to 165 °, preferably within the range from 20 ° to 160 ° is preferred, the range from 30 ° to 150 ° is more preferred, and the range from 45 ° to 135 ° is most preferred. The direction of the polymer particle product stream is understood as the direction in which the mass of polymer particles moves, which is the direction from the inlet through the fluidization chamber to the particle outlet, where a particular polymer particle flows. It is not the direction to move through the layers.

  A fluidized bed dryer compatible with the method of the present invention is shown in FIG. 1 and described in detail below.

  With the method of the present invention and a fluidized bed dryer compatible therewith, even if the temperature is well above about 200 ° C. (where the exothermic autolysis reaction of SAP is usually observed), Heat treatment can be performed in a safe and reliable manner. Furthermore, the fraction of washed polymer particles can be reduced, and a short residence time distribution of the polymer particles in the fluidized bed dryer can be obtained, so that permeability under CRC and AAP and under pressure (permeability under) For load (PUL) and saline flow conductivity (SFC), we guarantee a uniform, high-performance, high-quality product. Also, improved gas flow dryer design and operational details improve gas flow, resulting in lower energy consumption and avoid exothermic decomposition of polymer particles even at temperatures above 200 ° C. It becomes possible to do.

  The polymer particles preferably have a particle size ranging from 45 μm to 850 μm. The polymer particles are preferably particles called superabsorbent particles, that is, polymer particles capable of absorbing 0.9% saline solution 15 times its own weight.

  The polymer particles heat treated by the method of the present invention are obtained by polymerizing a monomer mixture comprising at least one ethylenically unsaturated monomer, at least one crosslinker, and at least one initiator. It is preferred that

  Suitable ethylenically unsaturated monomers are α-, β-unsaturated acids, preferably α-, β-unsaturated carboxylic acids or sulfonic acids, which include acrylic acid, methacrylic acid, crotonic acid, Isocrotonic acid, itaconic acid, fumaric acid, maleic acid and 2-acrylamido-2-methyl-1-propanesulfonic acid are included. Although these acids can be used in the acid form, the α, β-ethylenically unsaturated acid is at least partially neutralized in the form of a metal salt such as sodium salt or potassium salt and / or an ammonium salt. It is more preferable to use it.

  The polymerization can be carried out utilizing acidic monomers that are either not neutralized or wholly or partially neutralized prior to polymerization. Neutralization is preferably accomplished by contacting the aqueous monomer solution with an amount of base sufficient to neutralize 10% to 95% of the acidic groups present in the acidic monomers. Preferably, neutralization of 40% to 85% is sufficient for the amount of base, with 55% to 80% neutralization of the bases present in the monomer being most preferred. Compounds that are convenient and suitable for neutralizing the acidic groups of the monomers include bases that sufficiently neutralize the acidic groups without adversely affecting the polymerization process. Examples of such compounds include alkali metal hydroxides, alkali metal carbonates and alkali metal bicarbonates.

  The superabsorbent polymer particles are preferably at least about 10% by weight, more preferably at least about 25% by weight, and even more preferably from about 45% to about 99.9% by weight α-, β-unsaturated carboxylic acids and / or Alternatively, it can be obtained by polymerizing a monomer mixture consisting of sulfonic acids, wherein the acidic groups are preferably present at least partially in the form of sodium, potassium and / or ammonium salts. Is possible.

  Preferably, at least about 25 mol% of the acid groups are neutralized, more preferably at least about 50 mol%, even more preferably from 50 mol% to less than 90 mol%, more preferably from about 50 mol% to 80 mol%. % Is neutralized. The monomer mixture may be composed of a mixture of the suitable monomers. The monomer mixture may also contain additional ethylenically unsaturated monomers in amounts up to 60% by weight, such as acrylamide, methacrylamide, maleic anhydride, or alkyl esters and alkylamides of the above monomers, such as methyl (meth). It may be composed of acrylate, (meth) acrylamide, hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate, or (meth) acrylates of polyethylene glycol methyl ether, but is not limited thereto.

  The monomer mixture further comprises at least one crosslinking agent for crosslinking the polymer network, ie a network crosslinking agent. Suitable crosslinkers are those having at least two ethylenically unsaturated double bonds, at least one functional group reactive with at least one ethylenically unsaturated double bond and an acidic group, It has at least two functional groups reactive with acidic groups or a mixture thereof.

Suitable shared network crosslinking agent with respect to one _{molecule, CH 2 = CHCO-, CH 2} = C (CH 3) CO- and CH ₂ = CH-CH ₂ - is selected from the group consisting of 2 Includes compounds having from 1 to 4 functional groups. Examples of crosslinking agents include diallylamine; triallylamine; ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, Diacrylic and dimethacrylic acids of methylolpropane and pentaerythritol; triacrylates and trimethacrylates of trimethylolpropane and pentaerythritol; tetraacrylates and tetramethacrylates of pentaerythritol; allyl methacrylate; 3 to 30 ethylene oxide units Highly ethoxylated derivatives of trimethylolpropane or pentaerythritol with tetraallyloxyethane and Acrylate compounds include, for example, highly tetraacrylate and tetra methacrylate ethoxylated trimethylolpropane triacrylate or pentaerythritol. As other crosslinking agents, monoallyl ether polyether monoacrylates such as polyethylene glycol monoallyl ether acrylate (PEG-MAE-AE) are suitable. Particularly suitable are ester type crosslinkers, highly ethoxylated trimethylolpropane triacrylate (HE) in the range of about 3 to about 30 EO-units per molecule; HE -TMPTA), allyl type crosslinkers and crosslinkers having acrylate and allyl type functions in the same molecule, such as polyethyleneglycol monoallyl ether acrylate (PEG-MAE-AE).

  Polyethylene glycol can be used as a bifunctional or polyfunctional agent capable of forming a crosslink by reacting with an acidic group of the polymer backbone at a high temperature. Polyethylene glycol, such as PEG600, can be used at room temperature (23 +/−). 2 ° C) and is preferably liquid or pasty.

  These network crosslinkers should be distinguished from the surface crosslinkers described below and should not be confused. Mixtures of the network crosslinking agents already mentioned can also be employed.

  The network cross-linking agent renders the water-absorbing polymer insoluble, but at the same time it can also swell. The preferred amount of cross-linking agent is the desired degree of water absorption capacity and the strength desired to retain the absorbed liquid, ie adsorption against pressure (AAP) or absorption under pressure (absorption under pressure). load; AUL). The crosslinking agent is preferably used in an amount ranging from 0.0005% to 5% by weight, based on the total weight of the ethylenically unsaturated monomer used. More preferably, the amount ranges from 0.1% to 1% by weight. When an amount greater than 5% by weight is used, the polymer will usually have a crosslinking density that is too high and exhibits a low water absorption capacity. If the amount of crosslinker used is less than 0.0005% by weight, the polymer will usually have a crosslinking density that is too low, and when in contact with the absorbed liquid, the polymer becomes sticky and poor initial quality. Absorption rate is shown.

  The network cross-linking agent is preferably soluble in an aqueous solution of an ethylenically unsaturated monomer, but may optionally only be dispersed in the solution in the presence of a dispersant. Examples of suitable dispersing agents include carboxymethylcellulose suspension aids, methylcellulose, hydroxypropylcellulose and polyvinyl alcohol. These dispersants are advantageously provided at a concentration of from 0.0005% to 0.1% by weight, based on the total weight of the ethylenically unsaturated monomer.

  Preferably, one or more of the above crosslinking agents can be used in combination with at least a small amount of a polyhydric alcohol. Preferably, the monomer mixture further comprises at least one polyhydric alcohol as an additional crosslinker, and the amount of the crosslinker is at least 50 ppm, more preferably from 100 ppm to 1000 ppm, based on the total weight of the ethylenically unsaturated monomer. Is the amount. The polyhydric alcohol preferably contains glycerin, more preferably is composed of glycerin, and is preferably used in an amount of 100 ppm to 1000 ppm based on the total weight of the ethylenically unsaturated monomer.

  The monomer mixture from which the polymer particles are obtained further contains at least one polymerization initiator.

  Conventional vinyl addition polymerization initiators can be used for the polymerization of water-soluble monomers and crosslinking agents. In order to initiate the polymerization, free radical polymerization that dissolves sufficiently in the monomer solution is preferred. For example, water-soluble persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate, further alkali metal persulfates, hydrogen peroxide, water-soluble azo compounds such as 2,2′-azobis- (2-amidino Propane) hydrochloride and the like are available. Hydrogen peroxide or sodium persulfate, which is called a redox initiator system and can be used as an oxidizing component, can be used in combination with a reducing agent such as sulfites, amines, or ascorbic acid. The amount of initiator is preferably used in the range from 0.01% to about 1% by weight, preferably from about 0.01% to 0.5% by weight, based on the total weight of the ethylenically unsaturated monomer. Used up to a range.

In addition, the monomer mixture may contain one or more chelating agents to control the initiation rate or the polymerization rate, otherwise it will depend on impurities present in the monomer mixture, especially heavy metal ions such as iron ions. , Going up to an undesired level. The chelating agent can preferably be selected from organic polyacids, phosphoric acid polyacids and their salts. The chelating agents are nitrilotriacetic acid, ethylenediaminetetraacetic acid, cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol-bis- (aminoethyl ether) -N, N, N′-triacetic acid, N- (2-hydroxyethyl). ) -Ethylenediamine-N, N, N′-triacetic acid, triethylenetetraaminehexaacetic acid, tartaric acid, citric acid, iminodisuccinic acid, gluconic acid, and salts thereof are preferred. The most preferred chelating agent is the pentasodium salt of diethylenetriaminepentaacetic acid, which is commercially available in the form of an aqueous solution under the trade name Versenex ^™ 80 from Dow Chemical.

  The monomer mixture may also include graft polymers such as polyvinyl alcohol, starch, and water-soluble or water-swellable cellulose ethers. When employing such a graft polymer, the graft polymer can be used in an amount up to about 10% by weight, preferably based on the total weight of the ethylenically unsaturated monomer.

  Furthermore, the monomer mixture may contain recycled fine particles of a superabsorbent polymer. Fine particles are considered to be particles that are too small for the desired use as defined by the product specifications. The microparticles are generated by grinding the dried polymer gel after polymerization or by grinding the dry polymer. Thus, the undesired product fraction is removed from the polymer but can also be reused by incorporation into the monomer mixture prior to polymerization.

  The fine particle fraction can be determined by sieving using the EDANA standard test method WSP220.3 (10). The microparticles can also be obtained from a fraction washed by a method for heat treating SAP particles in a fluid bed dryer, preferably by the method of the present invention. With the hot gas flow, the particles are washed until they have a diameter of about 250 μm. Polymer particles having a particle size of less than 250 μm, preferably less than 200 μm are defined as fine particles in the present invention.

  Furthermore, other additives can be added to the monomer mixture. Other additives include organic metal chlorates, silica oxides, zinc oxides and other water-insoluble metal oxides, organic or inorganic water-insoluble powders, surfactants, dispersants, silver salts and other off-flavors. Can be selected from, but are not limited to, chemicals that suppress aging, water-soluble metal salts such as aluminum sulfate and aluminum lactate, magnesium salts and calcium salts, or further processing aids such as modified nonionic polypropylene waxes is not.

  Suitable methods for polymerizing these monomer mixtures to obtain water-absorbing polymer particles, especially SAP particles, are well known to those skilled in the art. Preferably, the polymer particles heat-treated by the method of the invention can be obtained by polymerizing the monomer mixture by the method described in co-pending European patent application 10003452.9.

  The polymerization reaction can occur in an aqueous solution or in a dispersed phase (that is, solution polymerization or suspension polymerization) in batch mode or continuous mode.

  In particular, when the polymerization reaction is carried out in an aqueous solution, the obtained polymer is preferably pulverized by grinding or the like, but a sieve is used to remove particles having a particle size of less than 45 μm or 850 μm or more before heat treatment. There is also an option to call.

  The polymer particles are preferably dried before being subjected to the heat treatment according to the method of the present invention.

  Preferably, the polymer particles heat treated by the method of the present invention, when subjected to heat treatment, have a residual moisture content based on the total composition as measured by EDANA standard test method WSP230.3 (10). Is preferably less than 12% by weight, more preferably in the range of 0.5% to 6% by weight, even more preferably in the range of 0.5% to 5% by weight.

  Preferably, in the lower plenum chamber of the fluidized bed dryer, at least one hot gas stream is directed to at least one gas distribution bottom plate, the direction being substantially perpendicular to the horizontal longitudinal axis. Thus, the polymer particles in the fluidized bed move without stopping during the heat treatment in the fluidized bed dryer operating continuously. In the present invention, the term “substantially orthogonal” includes all angles from 60 degrees to 120 degrees.

  The bottom plate of the fluidized bed dryer that operates continuously in the method of the present invention is preferably a perforated plate, and the holes of the plate have a unique shape, and the holes are not a regular cylindrical round shape. Moreover, the direction of the flow path is also different from usual. It is preferable that the holes of the porous bottom plate have a triangular to semi-elliptical shape and have a conical opening in the flow path direction. Preferably, the perforated plate used as the bottom plate or a part thereof is a microporous sheet (relative to the long hole sheet) or an aggregate of microporous sheets. A suitable microporous sheet is commercially available from Hein, Lehmann, Trenn-und Fordertechnik GmbH (Krefeld, Germany) under the trade name “CONIDUR®”. The shape of the holes with a special direction in these sheets has a horizontal airflow component and allows polymer particles to be directed along the generally horizontal longitudinal axis of the fluidization chamber. Instead of or in addition to a porous bottom plate with holes oriented in this way, a vibration drying chamber is used to move the polymer particles along the generally horizontal longitudinal axis of the fluidization chamber during heat treatment. It is also possible to do.

  After passing through the at least one gas distribution bottom plate, at least one hot gas stream enters the fluidization chamber where it contacts the polymer particles and heats and fluidizes them. Oriented holes preferably used in the gas distribution bottom plate allow at least one hot gas stream to pass through the stream of polymer particles moving along the generally horizontal longitudinal axis of the fluidization chamber, the angle of which is 15 It is from 165 ° to 165 °, preferably from 30 ° to 150 °, more preferably from 45 ° to 135 °, even from 60 ° to 120 °, most preferably from 75 ° to 105 °.

  For fluidized bed dryers operating in batch mode, microporous sheets without oriented holes are preferred.

Particularly in fluidized bed dryers operating continuously, in the process of the present invention, preferably a plurality of hot gas streams can contact the polymer particles. During the heat treatment, preferably the polymer particles are first brought into contact with a gas stream having a temperature T _{g1 in} the range from 100 ° C. to 320 ° C. as a first heating in the fluidized bed dryer and then maintained at the temperature. In order to contact a gas stream having a temperature T _{g2 in} the range from 100 ° C. to 280 ° C. Therefore, it is preferable that the fluidizing chamber of the fluidized bed dryer operating continuously includes a temperature rising zone and at least another zone for maintaining the temperature.

The first gas stream can be used to heat the polymer particles in a short time until the desired particle temperature T _p1 is reached. The temperature T _g1 of the first gas stream is preferably set to exceed 30 ° C. above the desired particle temperature T _p1, and is set to exceed 50 ° C. above that temperature in order to ensure a fast heating rate. Sometimes it is done. However, if the particles are in contact with a gas stream having a temperature about 30 ° C. or as high as 50 ° C. above the desired particle temperature for too long, decomposition can occur. Therefore, if the particles to the desired particle temperature T _p1 reached (approximately), it is lower than T _g1, preferably preferably contacted with a second gas stream having a temperature T _g2 still higher than T _p1 the polymer particles . Said temperature T _g2 is preferably in the range from 150 to 280 ° C., preferably not exceeding 20 ° C. of the desired particle temperature T _p , more preferably not exceeding 10 ° C.

When the temperature T _p1 is reached, the polymer particles are maintained at that temperature for the remaining total residence time, ie, the residence time in the fluidization chamber of the fluidized bed dryer, or are heated and maintained at the temperature T _p2 , Here, T _p1 and T _p2 are different from each other, but it is preferable that both are in the range from 170 ° C. to 245 ° C., more preferably in the range from 190 ° C. to 235 ° C.

The total residence time of the polymer particles in the fluidized bed dryer of the present invention, that is, the average time for the polymer particles to exist in the temperature rising zone and the temperature holding zone of the fluidizing chamber may be in the range of about 2 minutes to several hours. Preferably, it is in the range of about 4 minutes to about 60 minutes, more preferably about 10 minutes to about 40 minutes. The total residence time is composed of a heating period and an actual heat treatment time. Temperature ramp-up, that is, a first time period until the polymer particles are heated to the desired temperature T _p using a gas stream having a first temperature T _g1 well above the desired product temperature T _p Preferably lasts for about a few seconds, for example between 2 seconds and about 10 minutes, more preferably between 1 minute and about 9 minutes, most preferably between about 2 minutes and about 8 minutes. When the product reaches the desired particle temperature T _p , the actual heat treatment time is started and the temperature of the gas stream T _g2 is adjusted from time to time in order to maintain the desired product temperature. The actual heat treatment preferably lasts about 1 to 60 minutes, more preferably about 2.4 to 45 minutes, and even more preferably about 5 to 30 minutes.

The gas stream having the temperature T _g1 and the gas stream having the temperature T _g2 have the same or different compositions, and can be supplied to the lower chamber through the same or different inlets. Further, the polymer particles can be further treated with one or more gas streams having a temperature T _gn , where n is 3, 4, 5, etc., and the temperature T _gn is different from T _g1 or T _2. .

  The method of the present invention makes it possible to obtain heat-treated particles having a short residual time distribution. Of the polymer particles discharged from the fluidization chamber of the fluidized bed dryer after the heat treatment, preferably at least 50% by weight, more preferably at least 70% by weight, and most preferably at least 80% by weight is the planned heat treatment time t ±. Heat treated within 5%.

  In the method of the invention, the pressure drop across the gas distribution bottom plate, i.e. the difference between the pressure on the plenum side of the plate and the pressure on the fluidization chamber side is preferably in the range from 100 Pa to 900 Pa, more preferably 150 Pa. To 400 Pa, most preferably between 200 Pa to 300 Pa. In view of the approaching gas velocity and operating temperature, the bottom plate manufacturer provides a pressure drop curve to select an appropriate bottom plate to obtain the desired pressure drop. The total pressure drop in both the bottom plate and the fluidized bed can preferably range from 2.500 Pa to 5.000 Pa. The total pressure drop is measured by at least one differential pressure transmitter provided 60 cm below the bottom plate with respect to the pressure outside the fluidized bed dryer. Suitable differential pressure transmitters are commercially available, for example from Emerson Process Management GmbH & Co. OHG (Wessling, Germany) under the trade name ROSEMOUNT. The pressure drop depends inter alia on the gas distribution bottom plate used, the temperature of the gas, the inflow rate and is well known to those skilled in the art. Guides for selecting a special perforated bottom plate for obtaining a specific pressure drop at a given temperature and a given inflow rate can be obtained from the manufacturer of said perforated bottom plate.

  In the method of the present invention, the height of the fluidized bed is preferably in the range from 10 cm to 80 cm, more preferably from about 30 cm to about 60 cm. The height of the fluidized bed can be controlled, inter alia, by the volume of approaching gas per hour and the pressure drop, which is well known to those skilled in the art.

  As the gas, any gas inert to the polymer under the employed conditions can be used, and examples thereof include nitrogen, carbon dioxide, rare gases, air, and a mixture thereof. Water vapor may be used as long as condensation of moisture is prevented and contact between the heat-treated polymer particles and the condensate is prevented. In the method of the present invention, air is the preferred gas for economic reasons. After fluidization through the layer of polymer particles, the gas stream is filtered and directed to the fluidization chamber, so that at least a portion of it is recycled, while the other portion is preferably released to the atmosphere.

  Using the method of the present invention, (i) "untreated" polymer particles, i.e. polymer particles that have been formed by polymerization, drying, grinding, sieving and have not been in contact with further solid or liquid material, ( ii) polymer particles whose surfaces have been rewet with pure water, (iii) polymer particles treated with a coating solution containing no surface cross-linking material, and (iv) polymer particles treated with a solution containing surface cross-linking material. It becomes possible to process.

  Preferably, a solution comprising at least one organic and / or inorganic crosslinking agent can be applied to the surface of the polymer particles before the particles are heat treated by the method of the present invention. The solution is preferably applied by spraying on the surface of the polymer particles, and more preferably spraying at a temperature ranging from 0 ° C to 99 ° C.

  Surprisingly, it was found that the properties of the product can be improved by re-wetting the surface of the polymer with aqueous solution particles prior to heat treatment, even in the absence of surface crosslinker, in distilled water, deionized water It is preferable to use water or “pure water” such as tap water, that is, water that does not contain a considerable amount of extraneous components such as toxic components, cross-linking components, and other active components, and the equivalent amount is preferably less than 100 ppm. Amount. Accordingly, in the method of the present invention, the polymer particles are preferably 0.3% to 7% by weight, preferably 1% to 5% by weight, more preferably 1.5%, based on the total weight of the polymer particles before heat treatment. Moisten the surface with an amount of water ranging from wt% to 3.5 wt%.

  Surprisingly, when the step for applying water or a solution containing a coating agent and / or a surface cross-linking agent is carried out in two stages, that is, the particles are not inside the fluidized bed dryer but in the fluidized bed dryer. It was found that even better results can be obtained if water or each solution is applied to the particles using a Wurster type or Glatt-Zeller type fluidized bed dryer before flowing and heat-treated particles.

  All liquids or solutions must be distributed substantially uniformly on the surface of the polymer particles. One suitable method is to add the liquid / solution in a suitable mixer, preferably sprayed onto the stirred polymer particles. The literature describes various suitable mixers such as screw mixers, paddle mixers, disc mixers, plow shear mixers and shovel mixers. Particularly preferred are vertical mixers, especially proshear mixers and shovel mixers. Suitable mixers are commercially available under trade names such as Lodige (R) mixer, Bepex (R) mixer, Nauta (R) mixer, Processall (R) mixer, Schugi (R) mixer, and the like. Suitable spray nozzles and atomization systems are well known in the prior art and are described, for example, in Zerstaubungstechnik, Springer Verlag, VDI-Reihe, Giinter Wotzmer (2002). As the monodisperse and polydisperse atomization systems, pressure nozzles, rotary atomizers, ultrasonic atomizers, impact nozzles, and the like can be used, but are not limited thereto.

  The coating solution preferably comprises a surface cross-linking agent in an aqueous solvent, ie a mixture of water and at least one water-soluble organic solvent, which is preferably a polyhydric alcohol, a polyglycidyl compound, a cyclic carbonate, a polyamine. , Alkoxysilyl compounds, polyaziridines, polyamidoamines, oxazolidones, bisoxazolines, water-soluble polyvalent metal salts such as magnesium, calcium, barium, aluminum lactates, hydroxides, carbonates, or Bicarbonates, or mixtures thereof, preferably selected from the group consisting of aluminum lactate, metal oxides or mixtures thereof.

In the present invention, the aqueous solvent is composed of both “pure” water and a mixture of water and a water-soluble cosolvent, and the water-soluble cosolvent includes methanol, ethanol, n-propanol, isopropanol, n-butanol, sec. - _C 1 -C ₆ alcohols and the like butanol and tert- butanol, ethylene glycol, 1,2-propylene glycol, or _C 2 -C ₅ diols such as 1,3-propylene glycol and 1,4-butanediol, Consists of acetone, etc.

  The surface cross-linking agent is preferably applied to the polymer particles in the form of an aqueous solution, and the solution contains one or more surface cross-linking agents from 100 ppm to 10,000 ppm, more preferably from 500 ppm to 5000 ppm. Preferably, the aqueous solution in an amount of from about 0.3% to about 10% by weight, more preferably from about 1% to about 6% by weight, based on the total weight of the polymer particles, Preferably about 2% to about 4% by weight of the aqueous solution is added to the polymer particles. Co-solvents and other liquid or dissolution additives can be added to the polymer particles as part of the aqueous solution or as a separate step before or after the addition of the aqueous solution containing the surface cross-linking agent.

  Further, the coating solution may contain additional components such as a crushing aid including polyoxyethylene (20) sorbitan monolaurate.

  After being treated with the coating solution as described above, the coated polymer particles are immediately subjected to the heat treatment method of the present invention, or a temperature of 0 ° C. to 99 ° C. before the heat treatment method of the present invention is performed, Preferably, it is kept at room temperature (+/− 23 ° C.). The incubating is preferably carried out under mixing in a separate container, that is, a container other than the inside of the fluidized bed dryer.

  In many cases, such a holding period (incubation at a constant temperature) ensures that the coating solution diffuses to the particle surface, and the cross-linking agent on the polymer particle surface is more uniformly dispersed. During holding, the temperature is preferably in the range of 0 ° C. to 99 ° C., and the holding time is preferably in the range of 10 seconds to 10 hours. A retention time of less than 10 seconds usually cannot guarantee a uniform dispersion of the coating solution and / or sufficient penetration of the coating solution into the particle surface. Also, the coated polymer particles may still be too wet, so the fluidized bed dryer cannot be effectively fluidized. On the other hand, if the holding time exceeds 10 hours, the surface crosslinking agent usually diffuses to the core of the polymer particles and is too far away from the surface, leading to poor quality after subsequent heat treatment.

The present invention further provides a fluidized bed dryer that is particularly adapted for use with the method of the present invention. Accordingly, the present invention further relates to the use of a fluidized bed dryer for heat treating water-absorbing polymer particles in continuous mode or batch mode, preferably by the method of the present invention as described above, wherein the fluidized bed dryer comprises:
i) a drying chamber having a substantially horizontal longitudinal axis;
ii) a particle inlet for supplying the particles to be treated to the fluidization chamber;
iii) a particle outlet for removing the treated particles from the dryer;
iv) at least one gas supply inlet in the plenum for supplying gas to the plenum;
v) at least one gas outlet for exhausting the gas stream from the drying chamber after flowing and passing through the particle bed,
The drying chamber is
A fluidizing chamber that opens downward into the lower plenum chamber;
A lower plenum chamber via at least one gas distribution bottom plate;
-At least one gas distribution bottom plate having an opening formed for upward gas flow from the lower plenum chamber into the fluidization chamber;
including.

  In particular, if the surface is still sticky and the surface-coated polymer particles are fed to a fluidized bed dryer, the particles may condense and the product may be insufficiently fluidized. is there. As a result, the polymer particle material remains on the hot gas distribution bottom plate and overheats, and the fluidization disturbance inhibits all appropriate heat exchange and starts exothermic decomposition. This ultimately leads to product decomposition and in some cases may lead to ignition. These risks are avoided using the fluidized bed dryer of the present invention for heat treating water-absorbing polymer particles, an example of which is shown in FIG.

  The fluidized bed dryer generally comprises a fluidizing chamber 1, a perforated bottom plate 3, preferably a fine hole plate such as a CONIDUR® plate, and a hot air distribution chamber (plenum 2) below the bottom plate 3. . The dryer comprises a product filling system 5 and a product discharge system 6, at least one hot gas heater 7, a suitable hot gas conduit 9 and an exhaust system for the gas stream passing through the fluidized bed. The exhaust system comprises a suitable filtration system 8 for recovering the washed polymer particles in the exhaust gas stream. The system preferably comprises a plurality of gas heaters 7a and 7b so that different temperatures can be set in different fluidized bed zones.

  After the gas is heated to the desired temperature, it is led to the plenum 2 where it is uniformly dispersed and flows through the openings in the bottom plate 3 to uniformly fluidize and heat the polymer material in the fluidization chamber 1. It is designed to flow uniformly at a speed of. After fluidizing and passing through the fluidized bed polymer layer, the gas stream is filtered and part of it is recycled while the other part is released to the atmosphere.

  For economic reasons, it is preferred that the heat treatment of the polymer particles be carried out in a continuous mode, but the fluidized bed dryer can also operate in a batch mode.

  Fluidized bed dryers are usually made of steel, but in principle can be any inert material that can withstand the high temperatures used and is mechanically stable. The shape of the fluidizing chamber can be cylindrical, conical or rectangular. A rectangular dryer is particularly preferred. Suitable sizes for production-scale rectangular fluidization chambers are, for example, lengths from about 4 m to about 8 m, preferably from about 5 m to about 7 m, more preferably from about 5.75 m to about 6.25 m. It is. The width ranges, for example, from about 0.7 m to about 2.1 m, preferably from 1.0 m to 1.8 m, more preferably from 1.3 m to 1.5 m. The height of the fluidizing chamber is preferably in the range of about 1 m to 3 m, preferably in the range of about 1.5 m to 2.5 m, more preferably in the range of about 1.85 m to about 2.15 m. The ratio of the length to the width of the gas distribution bottom plate is preferably in the range of 3 to 5.5, and the ratio of the area of the bottom plate to the height of the fluidization chamber is in the range of 2.5 to 5.5. The inside is preferable.

  In continuous mode, the product is continually fed to the end of the fluidizing chamber, which is rectangular, if necessary, by weight flow or volume flow from there for specific vibrations and / or special bottom plate holes. It can be carried along the fluidization chamber to the opposite side by the conditioned gas flow given by the design of and then discharged into the adjacent cooling chamber. In some cases, a separate product cooler may be used. After cooling, the product may be recovered from the cooling chamber or product cooler and packaged for shipping or further processing.

  The bottom plate may preferably be at least one microporous sheet as already described above and serves to hold the fluidization chamber particles and distribute the hot gas stream. The bottom plate separates the plenum from the fluidization chamber and is made of metal or other refractory material that provides the required stability and is perforated to allow hot gas flow to pass through. The plurality of holes preferably have a special size and shape as described above so that particles do not enter the plenum through the plate. The number of holes per unit area and the open cross section provided in the bottom plate require the desired amount of gas to transfer the required energy to the product and fluidize the product layer of the plate. It passes through the opening at a speed.

  The bottom plate of the fluidized bed dryer is made of a single sheet with a uniform structure over the entire area with respect to the hole size, hole design, number of holes per unit volume, etc., or specified in different areas of the fluidized bed dryer In order to provide fluidization and product movement, the bottom plate may be assembled from a plurality of sections, each section having a different design as required.

  The thickness of the bottom plate is preferably in the range of 0.3 mm to 5 mm. The opening of the bottom plate can have a spherical shape, a rectangular shape, an elliptical shape, etc., and has a shape suitable for directing the fluidized product in a desired direction by directing the gas flow. It is preferable. These dimensions depend on the particle size of the product being processed and the conditions required and are usually in the range between 0.1 mm and 0.5 mm, preferably 0.2 mm to 0.4 mm, Preferably it exists in the range from 0.3 mm to 0.35 mm. The size, number and design of the holes must be chosen so that the gas velocity and pressure drop of the fluidizing gas passing through the bottom plate are within the proper range for optimal and uniform fluidization. Well known to contractors.

  As already mentioned, it is important that all the material of the fluidization chamber is fluidized uniformly and constantly over the entire area of the bottom plate. The exothermic self-decomposition of the polymer particles can be reliably controlled up to a temperature of about 240 ° C. if proper heat exchange is achieved by the fluidization of the product layer evenly and self-acceleration of the decomposition is prevented. .

  Not only can the polymer inside the fluidization chamber break down, but there is also a high risk of accidental intrusion into the plenum and ignition of the unfluidized polymer material. Further, the product inside the plenum may block fluidization at the top of the bottom plate as it may block the bottom plate opening from below when sprayed onto the plate. Every care must be taken to ensure that the product does not leak from the upper fluidization chamber into the plenum due to defects or improper vent stream filters, or that the product is carried into the plenum by recycled airflow. Don't be. Appropriate equipment, such as a pressure monitor in the plenum below the bottom plate and / or a particulate monitor in the main air circulation line, can be used to keep you informed of any processing difficulties. It is essential to prevent the possibility of decomposition.

  Large product particles and all product aggregates that enter or are formed in the fluidization chamber remain unfluidized by their own weight. They remain in contact with the hot bottom plate and decompose or ignite unless removed sequentially. Therefore, as described below, such large particles or lumps must be removed from the system or prevented from forming internally.

  The polymer particles are constantly filled into the fluidization chamber at the desired rate, which can be controlled by a rotary valve or other suitable system. The feed polymer preferably has a temperature of about 50 ° C. or less upon entering the fluidized bed feed zone. Under conditions where the feed area is hot, almost all residual moisture in the particles (ie less than 12% by weight, usually about 0.5% to 6% by weight in EDANA method WSP230.3 (10)) is rapid. To be lost. Moisture is usually absorbed by the hot gas and released by the vent stream. The cooling zone or surface that can exist in the fluidization chamber creates a risk of moisture condensation, which creates a moistened area that adsorbs polymer dust and fine particles to form agglomerates and lumps. These lumps sometimes peel off and fall to the bottom plate. Some of such supply systems (feed pipes, rotary valves, etc.) installed inside or at least in contact with the fluidization chamber are constantly cooled by the feed material, causing condensation and agglomeration, Providing a cooling surface to form. Since the cooled product stream itself provides a cooling zone for condensation, there is a risk of causing unwanted agglomeration. In order to prevent the formation of agglomerates in the feed area, care must be taken. First, it is possible to install a device that assists in uniformly distributing the feed stream over a wide area of the hot fluidized bed. Next, some of such supply systems (supply pipes, rotary valves, etc.) installed inside or at least in contact with the fluidization chamber may be subjected to trace heating to prevent surface cooling. Can be provided. Furthermore, it is also possible to further prevent the occurrence of condensation by directing the dried air stream toward the inlet region.

  A special device for uniformly distributing the supply has a shape such as “chinese hat” 15, for example, and is installed in the fluidization chamber directly below the particle supply flow inlet. . As shown in FIG. 2, the device comprises a half-cone plate aligned with a jacket for electrical tracing.

To ensure operation, fluid bed dryers with dimensions as specified above have a bottom plate per m ² , from about 50 kg / h to about 2000 kg / h, preferably about 100 kg / h. from up to about 1000 kg / h, more preferably is feedstream packing of the product from about 125 kg / h to about 450 kg / h, also about 300 kg / h to about 3000 kg / h per unit m ^2, preferably about A total hot gas volume flow from 500 kg / h to about 2500 kg / h is charged. The gas stream still has a significant energy fraction even after passing through the product layer and is preferably regenerated to heat the particles. Thus, after separating the washed object by filtering with a suitable heat-resistant filter or cyclone, a portion of the gas stream is sent back to the heater (reused). However, as the amount of moisture contained in the hot gas stream increases due to water vapor from the feed, a portion of the gas stream must be discharged into the vent stream and refilled with dry fresh gas. The fresh gas can be utilized to fluidize and cool the hot SAP in the cooling chamber before mixing with the hot gas stream that has passed through the product layer. The proportion of the gas released out of the fluidization chamber is in the range of about 10% to about 40%, preferably in the range of about 20% to about 30%.

  Usually, a 1% to 15% by weight product stream needs to be carried (elutriated) by the gas stream and separated from the gas. It is very important to separate all particles from the gas stream efficiently and reliably, otherwise the particles are transported to the plenum by the recycled hot air and condensed there over time . Separation from the gas stream can be achieved by one or more cyclones, suitable filters, or a combination of both.

  Filter cyclones with special polyimide filters or Teflon filters suitable for temperatures above 190 ° C. are available for successful separation of particulates from gas streams. The pressure drop between filters, that is, the pressure before and after the filter is determined by the type of filter used and the cleaning cycle of the filter. If the pressure drop is too high, the speed of the total air circulation flow will be adversely affected, eventually causing inadequate fluidization and heat transfer efficiency. In order to prevent degradation of the product, the function of the filter must always be properly managed.

  The heating rate of the polymer depends on the energy uptake rate provided by the hot gas flow and the thickness of the product layer. Because of the above limitations on the energy uptake rate (gas temperature, gas rate), the rate of temperature rise is usually governed by the layer thickness. The preferred thickness of the fluidized bed depends on the size and shape of the fluidized bed dryer. A rectangular fluidized bed dryer operating continuously on a plant scale preferably has a (fluidized) bed height in the range from 10 cm to 80 cm, preferably from 30 cm to 60 cm. The height of the bed can preferably be managed by a weir at the discharge end of the fluidization chamber. If the bed height exceeds 80 cm, the rate of temperature rise will be too low and the product quality will be insufficient. If the bed height is too low, the pressure drop between the plenum and the product bed will be insufficient and fluidization will be uneven.

  The temperature rise of the fluidized bed can be promoted by energy supply by radiation. For example, one or more ultraviolet (UV) or infrared (IR) radiation sources can be attached to the fluidization chamber. In order to accelerate the rate of temperature rise of the product, the irradiation source is preferably installed in the feed zone of the fluidization chamber. Such a heat source is particularly desirable when operating conditions are met such that the hot gas stream cannot provide sufficient heat supply for an adequate rate of heating.

  The particles are preferably processed one by one in the fluidization chamber in approximately the same way, and it is therefore desirable for each particle to have the same residence time in the fluidization chamber. Therefore, a semi-plug flow is desirable. In a standard fluidization chamber, considerable backmixing occurs, resulting in an undesirably wide product residence time distribution, while the particle fraction before being heat treated in the desired time span is discharged from the fluidized bed dryer, Other fractions are exposed to high temperatures for extended periods at the polymer degradation limit.

  In order to minimize backmixing, the baffle plate 16 can be inserted into the fluidization chamber 1 to achieve forced particle flow direction and quasi-plug flow, with a narrow retention in the fluidization chamber. A time distribution (FIG. 3) is provided.

  The height of the fluidized bed can be managed by an adjustable weir 17 on the discharge side of the fluidization chamber 1. The fluidized bed dryer preferably further comprises a cooling chamber 4 adjacent to the fluidizing chamber 1, after passing through the fluidizing chamber 1, the heat treated polymer particles are discharged therein. Preferably, the cooling chamber 4 is partly separated from the fluidizing chamber 1 by the above-mentioned weir 17 so that the overflowing material directly enters the cooling chamber 4 where it is cooled to a temperature below 50 ° C. (FIG. 3). The cooling chamber can be equipped with a fresh air blower and a heat exchanger 12, such as a multi-tube water-cooled heat exchanger (FIG. 1). The fresh air for cooling passes through the high-temperature product in the cooling chamber 4 and cools, and then is supplied to the high-temperature vent stream and leaves the fluidized bed dryer.

Get the desired heat transfer, product quality and minimal particulate cleaning for effective heat treatment of polymer particles in a fluidized bed dryer, as well as ensure proper fluidization and safe operation of the product In order to do so, the ratio of gas flow to the product stream must be carefully adjusted. To meet all these requirements, fluidized bed dryer production scale for continuous operation, hot gases of the bottom plate 1m product stream ² per 100-2000kg / h, and the bottom plate 1m ² per 300-3000kg / h A stream feed is preferred.

A production scale fluidized bed dryer can be operated, for example, under the following conditions. Conidur® bottom plate area: about 8.4 m ² , total airflow: about 7000-9000 kg / h, product extrusion: about 2400-2500 kg / h.

  The fluidized bed dryer can be divided into a plurality of sub-zones (indicated by vertical lines in the drying chambers of FIGS. 1 and 2), and operating conditions can be individually installed and managed. Each zone may have its own gas heating system 7a-7x and hot gas flow 9a-9x. By utilizing such a subsystem, a specific profile, such as a specific temperature profile, individual bed height, etc., can be targeted along the fluidized bed dryer.

  The first zone is preferably used to achieve a fast temperature rise of the polymer particles. Thus, the high temperature gas flow rate at the inlet and the temperature of the (gas) stream 9a should be set as high as allowed, but the second zone (gas stream 9b) will cause the fluidized product to undergo the desired heat treatment. Since it is only used to maintain the temperature, the conditions of the second zone are set relatively relaxed. Separation of the area is achieved by two different hot air supply systems managed separately.

  Alternatively, a single burner is used to provide a hot gas stream, followed by splitting the hot gas stream and separating a portion of the second zone flow rate with a cooler fresh gas. It is also possible. Electronic heaters, gas heaters, vapor pressure heat exchangers, or other heaters with suitable heat exchangers can be used to heat the gas stream supplied to the plenum (feed stream).

When polymer particle decomposition occurs, CO gas and CO ₂ gas are released. In order to immediately detect an undesirable decomposition reaction, it is necessary to install a highly sensitive infrared CO / CO ₂ detection system in order to monitor at least the CO / CO ₂ concentration inside the vent stream exiting the fluidization chamber. it can. It is preferable that the CO / CO ₂ concentration in the gas supply stream and the vent stream is constantly monitored and the difference between the two is calculated. If the CO / CO ₂ level exceeds the trigger concentration, the system can issue an alarm via the production management system so that action can be taken immediately. For example, in order to immediately suppress an uncontrollable decomposition reaction or ignition inside the fluidized bed, in this case, the fluidized bed dryer can be washed with nitrogen (reference numeral 11 in FIG. 1). When the possibility of decomposition is detected, the system is cooled and flushed with nitrogen, safety conditions are obtained, and the system is restarted according to safety procedures and safety guidance.

  The pressure drop and fluidization product of the microporous plate can also be monitored constantly. An undesired pressure increase means that the micropores of the microporous plate are clogged or the hot air is blocked by deposits formed on the microporous plate. When a predetermined level is reached, a warning is issued and urgent action is taken to prevent product degradation from occurring.

  It is preferred that the filter pressure drop is always monitored for safety. On the other hand, too high pressures normally caused by clogging of the filter create a risk of clogging the hot gas stream, leading to inadequate fluidization of the product, while low pressures that can occur suddenly. The decrease is usually a sign of filter tissue damage. In such cases, certain materials will leak into the hot gas stream and be carried down the microperforated plate to the plenum, where product action will occur if appropriate measures are not taken. Cause decomposition.

Therefore, the fluidized bed dryer used in the present invention is further a device for heating one or more (i) particle inlets,
(Ii) An apparatus for separating purified particulates from a gas stream preferably formed by one or more cyclones or filters, or a combination thereof, discharged from a fluidization chamber;
(Iii) a plurality of baffle plates inside the fluidization chamber to minimize backmixing;
(Iv) means for monitoring the pressure drop by the device for separating purified particulates from the gas distribution bottom plate, the fluidized bed and / or the gas stream;
(V) at least one irradiation source in the fluidization chamber;
(Vi) to measure the concentration of carbon monoxide and / or carbon dioxide in the gas stream leaving the fluidization chamber (vent stream) and optionally in the hot gas stream fed into the plenum (feed stream). Means of
(Vii) means for cleaning at least the drying chamber of the fluidized bed dryer with nitrogen or a rare gas;
It is preferable to provide.

  With the method of the present invention and a specially adapted fluidized bed dryer, it is possible to carry out a continuous heat treatment of the water-absorbing polymer particles in the fluidized bed, resulting in a high-performance and high-quality product. . In particular, as shown in the examples below, significant improvements are obtained in terms of CRC, the ratio of CRC to AAP (or CRC to AUL), and product quality to properties such as SFC and PUL.

  A further object of the present invention is thus heat-treated polymer particles obtained by the method of the present invention.

  In addition, if the method of the present invention and a fluidized bed dryer specially adapted to the present invention are used, it is possible to achieve a reduction in the fraction of washing and energy consumption during the heat treatment.

FIG. 1 shows a fluidized bed dryer specially adapted for the process of the invention. The fluidized bed dryer includes a drying chamber formed in the fluidizing chamber 1 and opening downward in the plenum chamber 2 through the gas distribution bottom plate 3. The cooling chamber 4 is adjacent to the end of the drying chamber, which is on the opposite side of the product inlet of the product filling system 5. The cooling chamber includes a heat exchanger 12. The product is discharged from the cooling chamber by a product discharge system 6. Gas heaters 7a and 7b are used to heat the gas stream entering the plenum 2 of the drying chamber, from which a hot gas stream is supplied to the drying chamber. After passing through the fluidized bed of the fluidization chamber 1, the vent stream is directed to the filtration system 8, where the washed polymer particles are separated from the gas and collected. A part of the filtered vent stream 9 is recycled to the gas heaters 7a and 7b, while the other part 10 is discharged to the atmosphere. The fluidized bed dryer may further comprise means 11 for cleaning the drying chamber with nitrogen or a noble gas. The fluidized bed dryer further comprises means for introducing the drying gas 14 into the cooling chamber 4. FIG. 2 shows a special device 15 for even distribution in the fluidizing chamber 1. FIG. 3 shows the function of the baffle plate 16 in the fluidization chamber 1 for obtaining a semi-plug flow of polymer particles. The weir 17 functions to adjust the height of the fluidized bed in the fluidizing chamber 1 and to separate the fluidizing chamber 1 from the cooling chamber 4. FIG. 4 shows the influence of the amount of particles on the heating rate according to each example of 4a to 4c.

DESCRIPTION OF SYMBOLS 1 Fluidization chamber 2 Plenum chamber 3 Gas distribution bottom plate 4 Cooling chamber 5 Product filling system / product introduction port 6 Product discharge system / product discharge port 7 Gas heater 8 Filtration system 9 Recycle filtration gas flow 10 Exhaust gas flow 11 Means for cleaning the drying chamber with nitrogen or noble gas 12 Heat exchanger 13 Fine particles separated and cleaned from the vent stream 14 Dry gas 15 Apparatus for even distribution 16 Baffle plate 17 Weir

1. Analytical method , centrifuge retention capacity (CRC)
Gravity measurement of liquid retention capacity in saline after being centrifuged by EDANA standard test WSP241.3 (10).

・ Adsorption to pressure (AAP) / Water absorption under pressure (AUP)
Gravity measurement of water absorption under pressure at pressures of 0.3 psi or 0.7 psi / 21 mbar to 49 mbar using polymer particles with a particle size in the range of 150 μm to 850 μm is the EDANA standard test WSP242.3 (10 ).

・ Water absorption under pressure at _{0.9 psi} (AUL _{0.9 psi} )
A nylon screen (50 × 50 mm ² ; 100 mesh / 149 μm) was placed on the perforated metal plate, followed by filter paper, and finally a hollow stainless steel cylinder having an inner diameter of 26 mm, an outer diameter of 37 mm, and a height of 50 mm. 167 mg of water-absorbing polymer particles were placed in a cylinder and evenly distributed. A nonwoven sheet with a diameter of 26 mm covered the polymer and was pressed with a 26 mm diameter plastic piston with a weight. The combined weight of the piston weight and the piston top weight is 328.2 grams, giving a load of 0.9 psi (62.1 mbar). The cylinder was soaked in 0.9% saline so that the nylon screen and the surface of the solution had the same height and the liquid absorption by the filter paper and the water-absorbing polymer particles was not subjected to water pressure. The particles were soaked for 1 hour. The plate was removed from the water bath and the liquid remaining in the holes in the metal plate and the nylon screen was sucked up with a paper tissue. The weight was then removed from the swollen gel and the gel was weighed. The weight of saline in which 1 gram of water-absorbing polymer particles is absorbed under pressure is called water absorption under pressure (AUI _{0.9 psi} ).

・ Soluble component (Extr.)
Measurement of the polymer content extractable by potentiometric titration was carried out using EDANA standard test WSP270.3 (10).

Residual acrylic acid (Res. AA)
The amount of residual monomers in the superabsorbent material, ie the amount of residual acrylic acid in the polyacrylic superabsorbent particles, was measured using EDANA standard test WSP210.3 (10).

・ Permeability under load (PUL)
The method used for measuring the water permeability under pressure is similar to the method for measuring AAP described above. To measure PUL, the AAP method described above was performed, and 0.9 g of superabsorbent particles were placed in the AAP cell to obtain a value of AAP _{0.7 psi (0.9 g)} . This method was then repeated at a weight of 5 g ± 0.005 g from the same highly absorbent material being tested to obtain a value of AAP _{0.7 psi (5 g)} . The PUL value is determined by the ratio of AAP _{0.7 psi (0.9 g)} / AAP _{0.7 psi (5 g)} x100.

・ Saline flow conductivity (SFC)
The methods described in US Pat. No. 5,562,646 and US Pat. No. 5,559,335 were used. In each test, 0.9 g aliquots of superabsorbent polymer particles with particle sizes from 150 μm to 850 μm were used.

・ Particle size distribution (PSD)
The size distribution of superabsorbent materials with a size up to 850 μm was measured using EDANA standard test WSP220.3 (10).

Moisture
Evaluation of residual moisture content of the superabsorbent material, that is, mass loss due to heating, was measured using EDANA standard test WSP230.3 (10).

・ Hunter color (Color L, a, b)
Hunter color was measured by ASTM E1164-94 and E1347-97. In this method, the color (reflectance) of the material is measured using a Hunter colorimeter. The sample color is described using three values. L correlates with “brightness”, and a and b mean the color axis. The value of a indicates redness, if negative, it indicates greenishness, and b indicates yellowishness, if negative, it indicates blueness.

2. Preparation of superabsorbent polymer-Preparation of polymer 1 The monomer solution was composed of 724.44 kg of sodium hydroxide, 371.73 kg of process water (partially demineralized groundwater), and 1401.3 kg of glacial acrylic acid (AA) ( 99,8%) in a batch mode. To this solution was added 3.63 kg of a 40.2% active solution of pentasodium diethylenetriaminepentaacetic acid salt (commercially available from Dow Chemical Company under the trade name Versenex ^™ 80), based on acrylic acid (based on acrylic acid; boAA) corresponding to 750 ppm, 10.32 kg of 5% sodium chloride active solution (265 ppm boAA), 11.68 kg of PEG600 (6000 ppm boAA), 598 kg of glacial acrylic acid (99.8%) and 6. A mixture of 23 kg of an average of 15 EO units of ethoxylated trimethylolpropane triacrylate (3200 ppm boAA) per molecule was added. During mixing, the temperature of the solution was controlled below 35 ° C.

  The monomer solution was then transferred to a horizontal uniaxial kneading reactor. During the transfer to the reactor, 1.3 kg of 30% hydrogen peroxide active solution (200 ppm b.o.AA) and 42.82 kg of 10% sodium persulfate active solution (2200 ppm b.o.AA) were mixed into the monomer solution. 368.1 kg of superabsorbent fine particles (18.4% b.o.AA) were added to the monomer solution and mixed uniformly. The resulting mixture was deoxygenated by washing with nitrogen. The temperature was then adjusted to 30 ° C. Under stirring, the polymerization was initiated by adding 36.1 kg of 1% sodium erythorbate active solution (185 ppm b.o.AA) to the reactor. When the polymerization was initiated, the reactor jacket and shaft temperatures were adjusted to 70 ° C. When the reaction mixture reached a temperature near 85 ° C., the reactor pressure was reduced to maintain the peak temperature at 85 ° C. When the peak temperature was reached, the polymer gel was cooled to 70 ° C. by further reducing the reactor pressure. The vapor was condensed in a condenser on the reactor and directed to the gel inside the reactor. Ten minutes after the peak temperature is reached, the granular polymer gel is transferred to a gently stirred holding tank for an average residence time of 100 minutes, from which it can be further sized in the extruder. Were continuously taken out, spread onto a belt of a belt dryer, and dried in hot air at 170 ° C. for 20 minutes. The polymer layer obtained was ground, ground in a rolling machine (Bauermeister) and sieved (0.15 mm to 1.18 mm) to give polymer 1.

-Preparation of polymer 2 The procedure described in the preparation of polymer 1 was repeated, but here 5.84 kg of HE-TMPTA (3000 ppm boAA) was used.

-Preparation of polymer 3 The procedure described in the preparation of polymer 1 was repeated but using here 4.28 kg of ethoxylated trimethylolpropane triacrylate (1900 ppm boAA) with an average of 15 EO-units per molecule.

  The properties of polymers 1 to 3 are summarized in Table 1a.

Table 1a : Properties of polymers 1 to 3 before heat treatment

Preparation of polymer 4 The procedure described in the preparation of polymer 3 was repeated, but the monomer formulation was free of chloric acid and 1.06 kg (220 ppm boAA) of an active solution of 40.2% diethylenetriaminepentaacetic acid pentasodium salt. Included. 30% hydrogen peroxide active solution (350 ppm boAA) is 2.28 kg, 10% sodium persulfate active solution (1400 ppm boAA) is 27.25 kg, and 1% sodium erythorbate active solution (220 ppm boAA) is 42. 82 kg was used.

Preparation of polymer 5 The procedure described in the preparation of polymer 4 was repeated, but using 2.8 kg of ethoxylated trimethylolpropane triacrylate (1443 ppm boAA) with an average of 15 EO units per molecule as the crosslinker. Then, as an additional network cross-linking agent, 5.42 kg of a 70% active solution (1950 ppm boAA) of polyethylene glycol monoallyl ethacryl acrylate (PEG-MAE-AE) having an average of 10 EO units per molecule was added.

-Preparation of polymer 6 The procedure described in the preparation of polymer 4 was repeated but using 2.4 kg of ethoxylated trimethylolpropane triacrylate (1235 ppm boAA) with an average of 15 EO units per molecule as the crosslinker. 5.64 kg of a 70% active solution (2030 ppm boAA) of polyethylene glycol monoallyl ethacryl acrylate (PEG-MAE-AE) with an average of 10 EO units per molecule was added.

-Preparation of polymer 7 The procedure described in the preparation of polymer 4 was repeated but using 3.27 kg of ethoxylated trimethylolpropane triacrylate (1685 ppm boAA) with an average of 15 EO units per molecule as the crosslinker. 6.47 kg of a 70% active solution (2330 ppm boAA) of polyethylene glycol monoallyl ethacrylacrylate (PEG-MAE-AE) with an average of 10 EO units per molecule was added.

-Preparation of polymer 8 The procedure described in the preparation of polymer 4 was repeated, but using 4.7 kg of ethoxylated trimethylolpropane triacrylate (2420 ppm boAA) with an average of 15 EO units per molecule as the crosslinker. 7.9 kg of a 70% active solution (2860 ppm boAA) of polyethylene glycol monoallyl ethacryl acrylate (PEG-MAE-AE) with an average of 10 EO units was added.

  The properties of polymers 4-8 before heat treatment are summarized in Table 1b.

Table 1b : Properties of polymers 4-8 before heat treatment

Preparation of polymer 9 The procedure described in the preparation of polymer 4 was repeated, but the monomer formulation was an average of 15 EO units of ethoxylated trimethylolpropane triacrylate (HE-TMPTA) per molecule (1443 ppm boAA). 2.8 kg and an average of 10 EO units of a polyethylene glycol monoallyl ethacryl acrylate (PEG-MAE-AE) 70% active solution (1950 ppm boAA) was included in 5.42 kg. Furthermore, 11% boAA superabsorbent fine particles were added to the monomer solution and mixed uniformly.

Preparation of polymer 10 The procedure described in the preparation of polymer 9 was repeated, but the monomer formulation was an average of 15 EO units of ethoxylated trimethylolpropane triacrylate (HE-TMPTA) per molecule (HE-TMPTA) (1235 ppm boAA) 2.4 kg, and 5.64 kg of a 70% active solution (2030 ppm boAA) of polyethylene glycol monoallyl ethacrylacrylate (PEG-MAE-AE) having an average of 10 EO units.

Preparation of polymer 11 The procedure described in the preparation of polymer 9 was repeated, but the monomer formulation was an average of 15 EO units of ethoxylated trimethylolpropane triacrylate (HE-TMPTA) per molecule (HE-TMPTA) (1685 ppm boAA) And 6.47 kg of a 70% active solution (2330 ppm boAA) of polyethylene glycol monoallyl ethacrylacrylate (PEG-MAE-AE) with an average of 10 EO units per molecule.

-Preparation of polymer 12 The procedure described in the preparation of polymer 9 was repeated, but the monomer formulation was an average of 15 EO units ethoxylated trimethylolpropane triacrylate (HE-TMPTA) (2420 ppm boAA) per molecule. And 7.9 kg of a 70% active solution (2860 ppm boAA) of polyethylene glycol monoallyl ethacryl acrylate (PEG-MAE-AE) with an average of 10 EO units.

-Preparation of polymer 13 The procedure described in the preparation of polymer 12 was repeated, but the monomer formulation was 70% of polyethylene glycol monoallyl ethacrylacrylate (PEG-MAE-AE) with an average of 10 EO units per molecule. 9.88 kg of active solution (3580 ppm boAA) was included and PEG 600 was not included.

  The properties of polymer 4 and polymers 9 to 13 are summarized in Table 1c.

Table 1c : Properties of polymer 4 and polymer 9 to polymer 13

-Preparation of polymer 14 The procedure described in the preparation of polymer 3 was repeated, but the concentration of ethoxylated trimethylolpropane triacrylate (HE-TMPTA) was changed to 2200 ppm boAA and 200 ppm boAA glycerin in the monomer solution. Added to.

-Preparation of polymer 15 The procedure described in the preparation of polymer 3 was repeated, but the concentration of ethoxylated trimethylolpropane triacrylate (HE-TMPTA) was changed to 2700 ppm boAA and 600 ppm boAA glycerin in the monomer solution. Added to.

  The properties of polymer 14 and polymer 15 are summarized in Table 1d.

Table 1d : Properties of polymers 14 and 15

Preparation of polymer 16 The monomer solution was 2925.67 kg of 25% active sodium hydroxide solution, 1495.13 kg of process water (partially desalted ground water), 1357.8 kg of glacial acrylic acid (AA) (99,9% active) was prepared by careful mixing. To this solution, 3.62 kg of 40.2% Versenex ^™ 80 active solution, 1.71 kg of 5% sodium chloride (265 ppm boAA) active solution, 22.61 kg of 60% PEG600 (7000 ppm boAA) active solution, A mixture of 581.9 kg of glacial acrylic acid (99.9% active) and 4.84 kg of an average of 15 EO-units of ethoxylated trimethylolpropane triacrylate (2500 ppm boAA) per molecule was added. In this monomer solution, 68.6% of acrylic acid was neutralized. During mixing, the temperature of the solution was controlled below 35 ° C.

  The monomer solution was then transferred to a horizontal uniaxial kneading reactor. During the transfer, 1.3 kg of 30% hydrogen peroxide active solution (200 ppm b.o.AA) and 42.82 kg of 10% sodium persulfate active solution (2200 ppm b.o.AA) were mixed with the monomer solution. 319.72 kg of superabsorbent fine particles (16.5% b.o.AA) were added to the monomer solution and mixed uniformly. The mixture was deoxygenated by purging with nitrogen. The temperature was adjusted to 30 ° C. and finally the polymerization was started by adding 36.1 kg of 1% sodium erythorbate active solution under stirring.

  After the start of polymerization, the reactor jacket and shaft temperature was adjusted to 70 ° C. When the reactants reached a temperature near 85 ° C., the reactor pressure decreased to maintain the peak temperature at 85 ° C. When the peak temperature was reached, the polymer gel was cooled to 70 ° C. by further reducing the reactor pressure. The vapor was condensed in a condenser on the reactor and directed to the gel inside the reactor. About 10 minutes after the peak temperature is reached, the granular polymer gel moves to a gently stirred holding tank for an average residence time of about 100 minutes, from which it can be further sized in the extruder. For this purpose, it was continuously taken out, spread on the belt of a belt dryer, and dried in hot air at about 170 ° C. for 20 minutes. The resulting polymer layer was pulverized and ground in a rolling machine (Bauermeister) and classified so as to obtain a polymer 16 having a particle size from 100 μm to 800 μm.

-Preparation of polymer 17 The procedure described in the preparation of polymer 16 was repeated, but the degree of neutralization was adjusted to 65%, the concentration of PEG600 was up to 5000 ppm and the concentration of recycled microparticles was up to 11% (all boAA) reduced.

-Preparation of polymer 18 The procedure described in the preparation of polymer 16 was repeated, but the concentration was changed as follows. PEG 600 was changed to 8000 ppm, HE-TMPTA to 2700 ppm, Versenex® 80 to 500 ppm, hydrogen peroxide to 350 ppm, and sodium persulfate to 1700 ppm. Furthermore, 200 ppm of glycerin (total concentration boAA) was added, but no fine particles were added.

-Preparation of polymer 19 All monomer solutions were neutralized to 31.74 parts acrylic acid (active content 99.9%), acrylic acid to about 65%, based on 100 parts final monomer solution 43.85 Prepared continuously from 1 part 25% aqueous sodium hydroxide and 15.63 parts water. To this mixture, 0.48 parts 5% Versenex ^™ 80 active aqueous solution (750 ppm boAA), 0.17 parts 5% sodium chloride active aqueous solution (265 ppm boAA), 0.07 parts HE-TMPTA (2200 ppm boAA), 0.37 parts of a 60% PEG 600 active aqueous solution (7000 ppm boAA) and 0.00636 parts glycerin (200 ppm boAA) were added. This monomer solution had a temperature of about 28 ° C. and a total solids content of about 38% and was continuously conveyed to the twin screw reactor at a feed rate of 6500 kg / h. In the feed stream, 0.26 parts 3% hydrogen peroxide active aqueous solution (250 ppm boAA), 0.79 parts 10% sodium peroxide active aqueous solution (2500 ppm active boAA), 7% superabsorbent particulates and about 13. A nitrogen flow of 5 kg / h was continuously injected. To the reactor feed zone, 0.84 parts of 0.7% sodium erythorbate aqueous solution was continuously added (each based on 100 parts of the final monomer solution). In addition, 70 kg / h of water vapor was injected from the bottom valve of the reactor. By reducing the reactor pressure to 850 mbar, the polymerization reaction inside the reactor was controlled and the peak temperature was controlled at 85 ° C. The evaporated water was condensed in the condenser at the top of the reactor and directed to the gel in reactor zone 3. A free-flowing granular gel is continuously discharged from the reactor into a holding tank, where it stays at 85 ° C. for about 1 hour, and is a die plate having 6 mm wide cuts arranged radially. Was chopped through and dried on a belt drier for 20 minutes with an air stream having a temperature of 170 ° C. After drying, the polymer layer was crushed in a rolling mill and sieved to obtain a particulate polymer having a particle size from 150 mm to 800 mm.

  The properties of polymers 16-19 are summarized in Table 1e.

Table 1e : Properties of polymers 16-19

Preparation of polymers 20-22 The monomer solution was prepared with 1263.67 parts 99.9% active acrylic acid and 1993.66 parts 24% active NaOH (resulting in a mixture temperature of always below 35 ° C). , Which is neutralized by about 68%) was carefully kneaded under cooling. To this mixture, 236.91 parts water, 18.94 g parts sodium sulfate, 2.9 parts HE-TMPTA (2300 ppm boAA), 12.62 parts 60% PEG600 active solution (6000 ppm boAA) Glycerin (250 mg / 200 ppm boAA for polymer 20, 500 ppm for polymer 21 and 1000 ppm for polymer 22) was added. Thereafter, 126.2 parts SAP microparticles (10% boAA) and 0.25 parts Versenex ^™ 80 (10 ppm boAA) were added.

  The mixture was kept at 22 ° C., during which time an initiator solution was prepared and deoxygenated. These initiator solutions were then fed to the monomer feed via a T-joint. The atmosphere in the polymerization reactor headspace was kept inert by continuous purging with a 200 L / h nitrogen flow. The reactor jacket temperature was set at 90 ° C. The monomer solution is continuously fed to the reactor at a temperature of 22 ° C. and at a rate of 6.5 kg / h (2.1 kg / L of total reactor volume), which is 20 L / h in a bubble column. Nitrogen stream, 35% hydrogen peroxide active aqueous solution (350 ppm active boAA), 10% sodium persulfate active aqueous solution (1700 ppm active boAA), 10% sodium carbonate, 2% NaOH and 0.7% Deoxygenated with 20% scrubber water containing sodium erythorbate active aqueous solution (200 ppm boAA). Scrubber water carbonate finished the deoxygenation and sodium ascorbate finally caused a rapid start of the polymerization reaction.

  At steady state conditions, the monomer feed is at least partially mixed with the polymer gel present in the reactor (average 1.7 kg), which polymer gel passes through the opening and end plate drains into the gel container. It was discharged continuously. The discharged gel is held under nitrogen for an additional 60 minutes and then further processed.

  The granular gel discharged from the reactor having a temperature higher than 60 ° C. was extruded from a kitchen-type meat grinder equipped with a die plate having an opening of 8 mm. A 800 g portion of the extruded gel is then placed in a basket consisting of a metal screen with 2 mm openings. The basket was placed in a lab size gel dryer and dried in a hot air of 5 m / s at a temperature of 180 ° C. for 20 minutes. The resulting dry polymer was ground in a rolling mill and sieved in a Lecce sieving tower equipped with sieves having a mesh size of 850 μm and 150 μm. The properties of polymers 20 to 22 are summarized in Table 1f.

Table 1f : Properties of polymers 20-22

3. Heat treatment in a fluidized bed dryer operating continuously , comparative example 1: Heat treatment of polymer 2 with continuous FBD using standard conditions Polymer 2 is produced in 10 months normal production, with a plate area of 8 m ² and 0 . Heat treated in a fluidized bed dryer with a substantially horizontal longitudinal axis with a fine perforated plate (Conidur plate, type 101, Hein & Lehmann, Germany) with 35 mm holes, giving a pressure loss of 270 Pa by hot air at a temperature of 260 ° C., The plate is divided into two zones and comprises two heat exchangers (one in each zone) for air heating and a cooling chamber. The weir to the cooling chamber was configured to give a fluidized bed with a height of 40 cm. The fluidized bed dryer operated with air as the fluidizing gas. The product temperature was set at 220 ° C. in the first zone and 230 ° C. in the second zone. In order to reach these temperatures, air is supplied to the plenum in zone 1 at a feed rate of 5650 kg / h (feed stream), at a temperature of 260 ° C., and air is supplied to the plenum in zone 2 at a feed rate of 3350 kg / h (feed stream). ), At a temperature of 235 ° C. Air at ambient temperature was introduced into the cooling chamber at a rate of 1450 kg / h and the same amount was discharged to the surroundings. Polymer 2 was fed to the fluid bed dryer at a feed rate of 1754 kg / h. After an average residence time of 40 minutes in the heating chamber, the product was cooled to a temperature of about 50 ° C. in the cooling chamber.

  During the 10 month production period, all 24 product degradations occurred in zone 1 of the fluidized bed dryer, so the degradation was stopped, the system was washed and soiled with brown or black degraded product particles The plant was shut down to separate the product. These undesired outages reduce 5% production capacity and 2.9% production based on total production.

Example 1: Heat treatment of polymer 2 with continuous FBD according to the present invention to provide a pressure drop of 530 Pa with a more suitable mold, eg hot air with a hole size of 0.3 mm and a temperature of 260 ° C. After changing the above-mentioned CONIDUR (registered trademark) microporous sheet types to 1 to 8 and optimizing the design of the fluidized bed dryer, heat treatment with FBD described in Comparative Example 1 was further applied to polymer 2. Continued for months. Other conditions were maintained, but air was supplied to the plenum in zone 1 at a feed rate of 5260 kg / h, supplying a surface air velocity of 0.35 m / s at a temperature of 260 ° C, and zone 2 Air was fed to the plenum at a feed rate of 2240 kg / h, a temperature of 235 ° C., and a heating rate of about 30 ° C./min. In a continuous production activity over 7 months, no degradation reaction was observed and neither production capacity nor production volume decreased.

Example 2: Heat treatment of polymer 1 with continuous FBD according to the present invention Polymer 1 was heat treated in a fluid bed dryer under the conditions described in example 1, but the polymer was 1050 kg / h in the fluid bed dryer. And the product temperature in the first zone was set at 205 ° C. at a heating temperature of 25 ° C./min and 215 ° C. in the second zone. In order to reach the product temperature, air is sent to the plenum in zone 1 at a feed rate of 5469 kg / h at a temperature of 246 degrees and to the zone 2 plenum at a feed rate of 3017 kg / h at a temperature of 235 ° C. sent. After an average residence time of 40 minutes in the heating chamber, the product was cooled to a temperature of about 50 ° C. in the cooling chamber. A representative sample was taken at the outlet of the fluidized bed dryer.

Example 3: Heat treatment of polymer 2 with continuous FBD according to the invention The procedure of example 1 was repeated, but polymer 2 was fed to the fluid bed dryer at a feed rate of 1050 kg / h in the first zone The product temperature was adjusted to 230 ° C., the heating rate was adjusted to 35 degrees / minute, and the second zone was adjusted to 228 ° C. To obtain these temperatures, the air to zone 1 is heated to 287 ° C and the air to zone 2 is heated to 232 ° C. The average residence time of the product in the heating chamber was 40 minutes. The product properties of the resulting products are summarized in Tables 2 and 3.

Table 2 : Properties of polymer 1 and polymer 2 after heat treatment

Table 3 : Particle size distribution of polymer 1 and polymer 2 after heat treatment

  Surprisingly, by utilizing the method of the present invention, it is possible to obtain a product having a desirable absorption capacity, a preferable CRC to AAP ratio, and a CRC for a soluble component, respectively, and a low residual monomer amount. Experiments have shown that this is possible. In particular, Example 3 further shows the advantage of using a hot gas stream temperature well above 200 ° C. and increasing the heating rate. High CRC and AAP values were achieved despite a slight decrease in crosslinker concentration compared to Example 2.

4). Change in heating rate Examples 4 and 5 were carried out in a batch-bed fluidized bed dryer of the experimental scale, type CTL (Allgaier-Werke KG, Wüngen, Germany), the dryer being 20 cm on the bottom side. A conical fluidization chamber having a diameter Conidur (registered trademark) micro perforated plate, a ventilator, an air heater, a fresh air filter and an exhaust filter, and a control box, the filter, if necessary, Can be dedusted with compressed air blast. This dryer does not circulate airflow.

  The fluidized bed dryer operating in batch was preheated by hot air of 5 m / s having the following temperature (intake air temperature). When the product area of the heater reached the desired temperature, a sample of polymer particles to be heat treated was filled and heated and fluidized by the hot air. When the product sample reached the target temperature Tp (such as 230 ° C.), fluidization and heat treatment were continued for the desired heat treatment time, eg, an additional 40 minutes. During the heat treatment, the intake air temperature was adjusted so that the product was maintained at the desired heat treatment temperature ± 2 ° C. When the heat treatment time had elapsed, the heat treated product was discharged to a metal tray and cooled to room temperature. The heat treatment time given in the example below is defined as the time range from when the product reaches the target temperature until the fluidization is complete and the particles are discharged for cooling.

Examples 4a-4c: Change in heating rate with the amount of polymer to be treated Different amounts of polymer 2 (a: 100 g, b: 500 g, c: 1,000 g) are described under item 4.1 The heat treatment was performed for 40 minutes according to the heat treatment procedure. The temperature in the product zone of the fluid bed dryer was recorded and illustrated in FIG. The results of Examples 4a-4c are summarized in Table 4.

  The results clearly show that the fast heating rate has a positive effect on the absorption capacity. As shown in FIG. 4, the heating rate is effectively influenced by changes in the amount of particles and bed height in the fluidizing chamber.

Table 4 : Results obtained in Examples 4a-4c

Examples 5a to 5c: Change in heating rate according to the intake air temperature Samples of polymer 2 (500 g each) were heat-treated for 25 minutes according to the heat treatment procedure described in Example 4, except that the intake air temperature is shown in Table 5 Changed on the street.

Table 5 : Results of Examples 5a-5c

  Also in this result, it was confirmed that the temperature elevation temperature had an effect on the product absorption capacity. As these experiments show, the intake air temperature is another means of managing the speed.

5. Surface cross - linking of dried polymer particles 5.1 Surface coating with ethylene carbonate (EC) aqueous solution A portion of 1 kg of dried and ground SAP is packed into a proshear mixer (Lodige) with a total volume of 6.1 L It was done. Under vigorous stirring, 31.6 g of 30% aqueous ethylene carbonate solution (9500 ppm based on dry SAP) was sprayed at room temperature onto the stirred product using a time spray nozzle. No further additives or postcrosslinkers were added. At the end of the addition, the rotating speed of the stirrer decreased and the wet product was held for an additional 15 minutes under gentle stirring.

5.2 Heat treatment in a small laboratory fluidized bed dryer Samples were heat treated in a small laboratory fluidized bed dryer and hot air was applied by a hot air gun (Bosch, Gerlingen, Germany). The fluidizing chamber is designed in a conical shape, having a lower diameter of 35 mm, an upper diameter of 60 mm, and a metal screen of 100 μm as a bottom plate. The fluidization chamber was covered with a lid with an opening, which was covered with a 100 μm metal screen. Two thermocouples are mounted for temperature measurement, one enters the hot air tube 1 cm below the bottom plate to measure the hot air intake temperature, and the other is the temperature of the fluidized product In order to measure, enter the fluidization chamber 3 cm above the bottom plate. Both the intake air temperature and the product temperature were manageable within a range of ± about 1 ° C.

For heat treatment, the fluidized bed dryer was preheated to the desired temperature (230 ° C., etc.) by applying hot air. When the temperature of the fluidization chamber reached the temperature, 30 g of product sample was loaded into the fluidization chamber (unless otherwise specified) and the sample was fluidized by hot air with the appropriate inlet temperature. During the first time period, the particles were heated at a rate of 45 ° C./min until the desired heat treatment temperature was reached (heating period). When the particles reached the desired heat treatment temperature T _p , the actual heat treatment time began and the intake air temperature was adjusted to maintain the desired particle temperature T _p . The heat treatment conditions at the desired temperature were maintained for 20 minutes unless otherwise stated. At the end of the heat treatment time, the hot air gun was turned off and the product was discharged and spread over the plate for rapid cooling.

・ 5.3 Sample heat treatment in an Erlenmeyer flask heated in an oil bath (oil bath method)
The heat treatment was performed in a 300 mL Erlenmeyer flask containing a magnetic stir bar (60 mm × 10 mm), and the flask was heated in an oil bath. The entire heat treatment system consisted of two identical components, each component having its own oil bath with a magnetic stir bar to heat and stir the polymer sample in its respective flask. A temperature management system was used to set and manage the oil bath and product temperatures as desired (± 2 ° C.). Usually, the temperature of the two oil tanks is different. One is used to raise the temperature of the polymer sample, and the other is used to keep the sample at the desired temperature T _p during heat treatment.

A 50 g portion of the coated superabsorbent polymer was charged into the flask and then into the preheated first oil bath. While gently stirring, the polymer is heated to the indicated temperature and then immediately moves from the oil tank 1 to the preheated oil tank 2 for the time indicated at the indicated temperature T _p . During this time, heat treatment was performed. The product was then removed from the flask and spread onto a plate for cooling.

Example 6
A sample of polymer 3 was coated as described in item 5.1 and heat treated at a particle temperature T _p of 180 ° C. applying the method described in item 5.2. The amount of sample used and the heat treatment time adapted are given in Table 6.

Table 6: Conditions and results of Example 6a and Example 6b

The results show that by surface postcrosslinking, polymers containing chloric acid can be successfully used to produce high quality SAP. When there are many samples, a longer heating time and heat treatment time are required. The ratio CRC / AAP _0.7Psi is therefore slightly inferior.

-Examples 7-11
Samples of polymers 4-8 (50 g each) were coated as described in item 5.1 above and heat treated using the method described in item 5.2. Details are summarized in Table 7.

Comparative examples 7-11
Examples 7-11 were repeated except that the heat treatment was carried out using the method described in item 5.3. Conditions and results are summarized in Table 8. Here, the abbreviations Ex and CE mean an example and a comparative example, respectively. In addition, the average parameters of the polymers obtained in Examples 6 to 11 (referred to as ΦEx6-11 in Table 7) are respectively compared with the average parameters of the comparative examples (refer to ΦCE6-11 in Table 7). , Respectively.

Table 7 : Conditions and results in Examples 6 to 11 and Comparative Examples 6 to 11

These results demonstrate the benefits of heat treatment in a fluid bed dryer. In the fluidized bed dryer, dramatically improved AAP _{0.7 psi} , PUL and SFC values (without the addition of polyvalent metal salts) were obtained.

Examples 12 to 19
The coating procedure described in Examples 6-11 was used, except that ethylene glycol (EG) or glycerin (Gly) was used as the surface crosslinker at the concentrations shown in Table 8. In these examples, polymer 5 was used.

Comparative Example 12 and Comparative Example 16
The procedures of Example 12 and Example 16 were repeated, respectively, but the heat treatment was performed using the method described in item 5.3. The experimental temperature conditions and results are summarized in Table 8.

Table 8 : Conditions and results in Examples 12 to 19 and Comparative Examples 12 and 16

  These data show that by heat treatment in the fluidized bed, high quality products can be obtained even in the presence of (post) crosslinker. In particular, it can be seen that by using a fluid bed dryer, superior PUL and SFC values can be obtained without compromising CRC, AAP or ratio CRC / AAP.

Examples 20 to 22
A sample of polymer 7 was coated and heat treated as described in Examples 7-11 above, except that the coating solution further contained aluminum lactate at a concentration of 2500 ppm based on the dry weight of the polymer. The experimental temperatures and results are summarized in Table 9.

Comparative Example 20
The procedure of Example 20 was repeated except that the heat treatment was performed using the method described in item 5.3. The experimental temperatures and results are summarized in Table 9.

Table 9 : Conditions and results of Examples 20 to 22 and Comparative Example 20

The results still show the advantage of using a fluid bed dryer for heat treatment. In particular, the values of PUL and SFC increased, indicating that the water permeability of the polymer has been improved. These data also show that a higher temperature rise (given by the higher intake air temperature _Tg1 ) dramatically improves the water permeability of the product.

  The above experimental results generally also show that by using a fluidized bed dryer for heat treatment, surface modifying additives such as aluminum salts and silica are no longer essential. This is an important point from the viewpoint of cost and process complexity. Further, since the heat treatment is performed with a paddle dryer, an additive for reducing the shearing force during the heat treatment is not required. A further important advantage of not using these additives is that they do not contaminate the airflow that is reused.

6). Surface wetting of already dried polymer particles. Examples 23-34
1 kg, part of the dried and ground polymer particles, was charged at room temperature into a Proshear mixer (Lodige) having a total volume of 6.1 L. Under vigorous stirring, 30 g of water was sprayed onto the stirred product using a spray nozzle. No further additives or postcrosslinkers were added to the product. The stirrer speed was then reduced and the wet product was held for an additional 15 minutes under gentle agitation.

  The samples were then heat treated in a laboratory small fluid bed dryer as described in item 5.2 except that 20 g of product sample was used and each sample was heat treated for 20 minutes. The conditions employed are given in Table 10. In Comparative Examples 23 to 29, Comparative Example 33, and Comparative Example 34, the polymer was not wetted.

Table 10 : Conditions adopted in Examples 23 to 34 and Comparative Examples 23 to 34

  Product samples from various experiments were analyzed and the results are given in Tables 11a-11c.

Table 11a : Results of Examples 23 to 34 and Comparative Examples 23 to 34

  These results show the surprising effect of prewetting the polymer particles before heat treatment to improve AAP and SFC during heat treatment.

Table 11b : Results of Examples 25-32 and Comparative Examples 25-32

  This result also shows the advantages of the present invention. Comparing the average of Comparative Examples 23 to 29 and the average of Examples 23 to 32, in the fluidized bed dryer, by moistening the particle surface before the heat treatment, the AAP after the heat treatment increased by about 4 g / g. Increases by 21 points and doubles the value of SFC (without any surface additives that promote water permeability!), While CRC remains substantially constant.

  Comparative Example 30 shows that a heat treatment temperature of 180 ° C. often does not give a product with the desired effect, but a higher temperature, often close to the decomposition temperature of the product, is required. .

  The beneficial effect of using a high ramp rate can be seen by comparing the results of Example 26 and Example 30. The higher intake air temperature used in Example 26 provides a higher heating rate, leading to increased values for AAP, PUL, and SFC. Moreover, the level of soluble component is also lowered.

Table 11c: Results of Examples 33-34 and Comparative Examples 33-34

  Similar to the polymers used in Examples 23 and 24, the polymers employed in Examples 33 and 34 contain chloric acid. Compared to the results of Example 23 and Example 24, these examples show that the addition of a small amount of glycerin has a positive effect on the soluble component concentration and SFC value of the heat-treated polymer particles. Yes.

7). Network cross - linking with a small amount of glycerin Example 35
100 g of polymer 18 was heat treated using the method described in item 4 at 230 ° C. for 15 minutes.

Comparative Example 35
500 g of polymer 16 was heat treated at 230 ° C. for 40 minutes using the method described in item 4.

Example 36
500 g of polymer 18 was heat treated at 230 ° C. for 15 minutes using the method described in item 4.

Comparative Example 36
Comparative Example 35 was repeated, but hot air with a gas velocity of 8 m / s was used.

Example 37
Example 35 was repeated, but hot air with a gas velocity of 8 m / s was used.

Comparative Example 37
500 g of polymer 17 was heat treated at 230 ° C. for 20 minutes using the method described in item 4.

Example 38
Example 38 was repeated, but 500 g of polymer was used.

Comparative Example 38
Comparative Example 35 was repeated, but hot air with a gas velocity of 8 m / s was used.

  The results of Examples 35 to 38 and Comparative Examples 35 to 38 are shown in Table 12.

Table 12 : Results of Examples 35-38 and Comparative Examples 35-38

Example 39
Polymer 19 was continuously fed to the fluidized bed dryer at a rate of 2400 kg / h and was heat treated according to the method described in Example 1 at a temperature of 230 ° C. and a weir height of 100 mm. A residence time of about 10 to 20 minutes at C. The resulting polymer particles possess the following properties: CRC 28.3 g / g, AUL _{0.9 psi} 23.3 g / g, ResAA 282 ppm, Extr. 6.5%.

This example uses a small amount of glycerin as a network crosslinker and uses a high heating rate at a heat treatment temperature above 200 ° C., so that even in the continuously operating heat treatment process of the present invention, a high AUL _{0.9 psi} is _achieved . It shows that the water-absorbing polymer particles can be obtained. The heat-treated product further contains very little soluble component and residual monomer.

Examples 40 to 46
An amount of 20 g of polymer 20-22 containing no chloric acid and containing glycerin was heat treated as described in item 4 and the inlet gas temperature Tg1 of 255 ° C. and the particle temperature Tp of 230 ° C. are shown in Table 13. Given for time t.

Table 13 : Results obtained in Examples 40-46

Comparing these results with those of polymers 16-18 containing chloric acid in Examples 35-38 (Table 12), Examples 40-46 have low CRC values, but AAP _{0.7 psi} has good values. It turns out that it is obtained. In addition, good or excellent PUL and SFC values can be obtained without adding surface modifiers such as polyvalent metal ions, and the soluble component of the heat-treated polymer containing glycerin is low. It can be an amount.

  Furthermore, if a polymer containing glycerin is used as a network cross-linking agent, only a very short residence time is required.

-Examples 47-52
Examples 40-46 were repeated, but immediately prior to undergoing the heat treatment, the surface of the polymer particles was moistened with a 3% by weight amount of water according to the method described in item 6. The results are shown in Table 14.

Table 14 : Results obtained in Examples 47-52

  As can be seen from the results presented in Table 14, when the surface of the polymer particles is moistened before the heat treatment, the water absorption performance of the particles is improved. In particular, the product permeability as shown by the PUL value and SFC value is dramatically improved.

Example 53
A sample of polymer 22 was surface coated using the method described in item 5.1. 50 g of the coated polymer particles were heat treated for 20 minutes as described in item 4, using an intake gas temperature T _g1 of 190 ° C. and a particle temperature T _p of 180 ° C.

Comparative Example 53
Example 53 was repeated except that a sample amount of 75 g of surface coated polymer particles was heat treated as described in item 5.3. Both the temperatures in the first and second oil tanks were set at 180 ° C., and heat treatment was performed for 69 minutes.

  The results of Example 53 and Comparative Example 53 are shown in Table 15.

Table 15 : Results obtained in Example 53 and Comparative Example 53

Even if a heat treatment time of 3 times is given, the excellent water immersion of the product indicated by the PUL value or SFC value obtained by using the method of the present invention cannot be obtained by the heat treatment by surface contact.

Claims (15)

A method for heat-treating water-absorbing polymer particles at a temperature T _p1 of 150 ° C. or higher, wherein the polymer particles have an initial particle temperature T ₀ of 50 ° C. or less in a fluidization chamber (1) of a fluidized bed dryer. To the temperature T _p1 at a heating rate of at least 10 ° C. per minute. The polymer particles are heated from the initial particle temperature T ₀ to the temperature T _{p1 in} less than 10 minutes, where T _p1 is preferably in the range of 170 ° C. to 245 ° C., more preferably in the range of 190 ° C. to 235 ° C. The method of claim 1 wherein:   The polymer particle is a monomer comprising at least one ethylenically unsaturated monomer, preferably acrylic acid present at least partially in the form of a salt, at least one crosslinking agent, and at least one initiator. The method according to claim 1, wherein the method is obtained by polymerizing the mixture.   The monomer mixture additionally comprises at least one polyhydric alcohol as an additional crosslinker and an amount of at least 50 ppm, preferably from 100 ppm to 1000 ppm, based on the total weight of the ethylenically saturated monomer. 3. The method according to 3.   The method according to any one of claims 1 to 4, wherein the polyhydric alcohol comprises glycerin, preferably composed of glycerin.   The polymer particles have a residual moisture content of less than 12% by weight, preferably from 0.5% to 6% by weight, based on the composition measured by EDANA standard test method WSP230.3 (10). 6. The method according to any one of claims 1 to 5, comprising:   Prior to heat treatment, the polymer particles may be from 0.3 wt% to 7 wt%, preferably from 1 wt% to 5 wt%, more preferably from 1.5 wt% to 3.5 wt%, based on the total composition. 7. A method according to any one of the preceding claims, wherein the surface is moistened with a range of amounts of water. After heat treatment at temperature T _p1 , the polymer particles are held in the fluidized bed dryer at temperature T _p2 , and both T _p1 and T _p2 are preferably in the range from 170 to 245 ° C., more preferably from 190. The method according to claim 1, wherein the method is within a range up to 235 ° C.   The method according to any one of claims 1 to 8, characterized in that the total residence time of the polymer particles in the fluidization chamber (1) is in the range of 5 to 60 minutes. Preferably, the solution comprising at least one organic or inorganic crosslinking agent by being sprayed at a temperature in the range of 0 to 99 ° C. before the particles are heated to the temperature T _p1 in the fluidized bed dryer. 10. The method according to any one of claims 1 to 9, characterized in that is applied to the surface of the polymer particles.   The solution is a polyhydric alcohol, polyglycidyl compound, cyclic carbonate, polyamine, alkoxysilyl compound, polyaziridine, polyamidoamine, oxazolidone, bisoxazoline, water-soluble polyvalent metal in an aqueous solvent. 10. The method according to claim 9, comprising at least one compound selected from the group consisting of salts, metal oxides or mixtures thereof. The particles are in contact with at least one hot gas stream having a temperature T _g inside the fluidized bed dryer and inside the fluidized chamber (1) of the fluidized bed dryer, the fluidizing chamber (1) At least 1 via at least one gas distribution bottom plate (3) having an opening formed for upward gas flow from at least one lower plenum chamber (2) into the fluidization chamber (1) The gas velocity at the surface of the hot gas stream in the fluidized bed is 0 l. 12. The method according to any one of claims 1 to 11, characterized in that it is in the range from 1 m / s to 0.57 m / s.   The pressure drop across the gas distribution bottom plate (3), ie the difference between the pressure on the plenum side of the plate and the pressure on the fluidization chamber side is in the range from 100 Pa to 900 Pa, preferably from 150 Pa to 400 Pa, most preferably The method according to any one of the preceding claims, characterized in that the total pressure drop across the bottom plate and the fluidized bed is in the range of 2.500 Pa to 5.000 Pa. Use of a fluidized bed dryer for heat treating water-absorbing polymer particles in a continuous mode or batch mode, preferably in the method of any one of claims 1-13,
The fluidized bed dryer is
i) a drying chamber having a substantially horizontal longitudinal axis;
ii) a particle inlet (5) for supplying the particles to be treated to the fluidization chamber;
iii) a particle outlet (6) for removing the treated particles from the dryer;
iv) at least one gas supply inlet in the plenum (2) for supplying gas to the plenum (2);
v) at least one gas outlet for exhausting the gas stream from the drying chamber after flowing and passing through a particle bed;
The drying chamber is
A fluidization chamber (1) opening downward into the lower plenum chamber (2);
A lower plenum chamber (2) via at least one gas distribution bottom plate (3);
At least one gas distribution bottom plate (3) having an opening formed for upward gas flow from the lower plenum chamber (2) into the fluidization chamber (1);
Use of a fluidized bed dryer characterized by comprising: Heat-treated polymer particles produced by the method according to any one of claims 1 to 13.

Images